Norepinephrine (NE) exerts diverse actions in visual and other neocortical areas. The collective actions of NE are important for coordinating peripheral sympathetic activities and goal-directed behaviors evoked by external stimuli. Three broadly based light and electron microscopic immunocytochemical studies are proposed to determine possible cellular substrates for the diversity of noradrenergic actions in the visual cortex. Specifically, the laminar distribution and subcellular sites of termination of catecholaminergic (CA) afferents and their relation to the B- adrenergic receptor (BAR) or one of four other putative transmitters, acetylcholine (Ach), GABA, neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) will be examined. Peroxidase- antiperoxidase and/or immunoautoradiographic labeling methods will be used to localize antigenic sites for antisera against the catecholamine- and acetylcholine-synthesizing enzymes, BAR and the latter three transmitters. Cat will be the primary experimental animal, because the vast majority of the literature on visual physiology and developmental plasticity has been established in this species. The specific goals are to determine: (1) whether the CA terminals exhibit heterogeneity in their relations to (a) the target sites (i.e. perikaryal vs dendritic vs axonal) or (b) the localization of BAR, (i.e. neuronal vs glial, presynaptic vs postsynaptic vs extrajunctional); (2) whether cholinergic terminals have specific cellular relations to CA terminals; and (3) whether neurons containing GABA, NPY or VIP show laminar variations in their cellular associations with CA terminals or other unlabeled neurons. By correlating the ultrastructurally identified sites of cellular associations and their relative frequencies with light microscopically identified laminar positions, the functional and cytoarchitectonic interrelationship of these transmitters should begin to emerge. This information is important for understanding the mechanism of vision and other modalities of sensory perception and may be of clinical relevance in understanding the consequences of sensory deprivation during development.